Track-type tractors may have an implement that moves a load such as soil, sand, rubble, construction materials, and other materials. One example is a bulldozer that includes a blade mounted on a front end of the machine for pushing, carrying, and moving a variety of loads. Tilt cylinders may be used to adjust the side-to-side tilt angle and the forward to back tilt angle (or pitch) of the blade, while one or more hydraulic lift cylinders may be used to raise and lower the blade as needed for moving the loads. Hydraulic lift cylinders may include a cylinder barrel that houses a piston rod. The head of the piston may be oriented toward the “head end” of the hydraulic lift cylinder, and the piston rod may extend to the “rod end” of the hydraulic lift cylinder.
Traditionally, the cylinder barrel is mounted high on a large elevated support structure, such as a radiator guard, that is attached to the front of the frame of the machine, while the piston rod is connected relatively low on the blade. Raising of the blade is carried out by contraction of the hydraulic lift cylinders, whereby hydraulic fluid flows into the rod end and applies pressure on the lower lip of the piston head (rod end pressure) to cause cylinder contraction. In a particular application known as pryout, this action is used to lift a bulk of material out of the ground in order to push it. In contrast, lowering of the blade is carried out by extension of the hydraulic lift cylinders, whereby hydraulic fluid flows into the head end and applies pressure on the piston head (head end pressure) to push the piston down through the cylinder barrel and cause cylinder extension. This action is used to force the blade edge into the ground, allowing the machine to dig and accumulate material.
However, the current mounting arrangement for hydraulic lift cylinders has many drawbacks. For one, it operates through cylinder contraction (rod end pressure) to raise the blade which has less capacity to generate force than cylinder extension (head end pressure). Cylinder extension has considerably greater capacity to generate force because the hydraulic fluid applies pressure to the upper surface of the piston head which has more surface area to act on than the lower lip of the piston head that is pressurized during cylinder contraction. Furthermore, those skilled in the art will appreciate that a bulldozer mechanism has its least mechanical advantage during blade lift. Thus, minimum mechanical advantage is combined with minimum cylinder capacity during blade lift in the current mounting arrangement. In order to meet pryout load requirements, the hydraulic system must be designed to be unnecessarily large for other blade movements. In addition, the elevated support structure used to mount the hydraulic lift cylinders results in a large bending moment on the frame, as well as a convoluted load path from the hydraulic lift cylinders to the support structure and the frame. Moreover, the large elevated support structure hinders access to the front of the engine. Even further, expensive and high-level machining is often needed for establishing the connections between the elevated support structure and the frame.
An alternative hydraulic lift cylinder mounting arrangement is described in U.S. Pat. No. 4,320,539. Specifically, the patent discloses hydraulic rams disposed between a frame supporting a snow-clearing blade on the front of a vehicle and a plate on the backside of the snow-clearing blade. Although effective, the hydraulic rams are not directly mounted to the frame of the vehicle, but to a separate frame that connects the vehicle to the snow-clearing blade. Thus, there is a need for improved hydraulic lift cylinder mounting arrangements for track-type tractors such as bulldozers.